1. Field of the Invention
The present invention relates to a p-type silicon single crystal and a method of manufacturing the same, and particularly to a p-type silicon single crystal manufactured with a Czochralski method and a method of manufacturing the same.
2. Background Art
A power device such as an IGBT (Insulated Gate Bipolar Transistor) has been widely used recently in home appliances, industrial machines, and the like. One of the primary characteristics of the power device is a high breakdown voltage, and substrates used for power devices in order to achieve this are required to be high in resistivity with a small variation thereof.
Silicon single crystals used for substrates for power devices are generally manufactured by the Czochralski method (“CZ” method). With the CZ method, since the segregation coefficient of dopants such as boron and phosphorus with respect to the silicon single crystal is less than 1, the dopant concentration in the silicon melt becomes greater as the silicon single crystal grows. Therefore, the dopant concentration in the grown silicon single crystal varies in the direction of the axis of growth, and consequently, the resistivity of the silicon single crystal also varies in the direction of the axis of growth. Thus, it has been difficult to control resistivity.
Regarding a technique for controlling resistivity of a single crystal, for example, Japanese National Patent Publication No. 2010-531805 describes a method for controlling resistivity of a silicon ingot used for manufacturing a solar cell. With this method, a silicon ingot is formed by preparing a metallurgical-grade silicon source material containing boron and phosphorus and adding aluminum or the like to metallurgical-grade silicon to fabricate a silicon melt. In this method, metallurgical-grade silicon containing a large amount of impurities is used as a silicon source material. Therefore, a resultant silicon single crystal substrate has resistivity as low as approximately 5 Ωcm or lower and it has been difficult to employ such a substrate for a power device required to have a high breakdown voltage.
In addition, in the metallurgical-grade silicon source material above, boron and phosphorus are originally contained in the silicon source material. Then, the amount of boron and phosphorus is determined and a group III element is mainly added in accordance with the desired amount of boron and phosphorus. Thus, since one type of element is mainly used as an element for controlling resistivity, it has been virtually impossible to reduce the variation in resistivity of the silicon single crystal substrate.